It has always been desirable to limit the amount of space taken up by electrical components. This allows for the creation of the smallest possible devices which employ those components. Where a device employs more than one electrical component it is also desirable to be able to pack those devices as closely as possible.
Typically, components are soldered to a printed circuit board and connections are provided by lines on the board. The board is then placed within a device housing.
Where it is desirable to minimize the volume of the device the printed circuit board is often dispensed with as it requires space. The components are then hardwired to one another. This is done especially where there is a relatively small number of components and connections within the device.
Both printed circuit board and hardwired connections require at least two solder joints for most electrical connections, one where each component is connected to the line or wire.
An example of such a demand for miniaturization is the hearing aid industry. The pressure for increasingly smaller volume hearing aids, or devices, has grown as hearing aids have shrunk from over the ear devices to in the ear devices, and more recently to in the canal devices. An in the canal device is concealed almost entirely within the ear canal. Only a small portion of the device is noticeable from outside the ear, and only on close inspection.
At least one manufacturer of components for such devices has responded by pairing components within a single component shell. This decreases the overall volume of the two components when compared to their volume as separate hardwired units.
Unfortunately, the placement of the components within a single shell does not allow for access to the components for repair, replacement or electrical adjustment. When one of the components is damaged the whole shell, including both components, is discarded.
In a hearing aid one of the components may be a receiver, otherwise known as a speaker, and the other an amplifier. The receiver is prone to break down much more readily than is the amplifier. This is due to the build-up of bodily secretions within the output port of the receiver. Amplifiers often cost a few dollars or more and it becomes expensive to discard both components when only one is faulty.
Additionally, placing both components in a single shell restricts electrical access to the components. At least one manufacturer uses a similar shell for its receiver/amplifier combination as for its receiver by itself. A receiver only shell typically has two or three supply or signal inputs. This is suitable for a receiver, however for maximum flexibility an amplifier may have other inputs. In addition to the above, it may be desirable to have frequency control, power control and gain trim inputs. These require direct connections for each input.
As well, a two component shell does not allow for replacement of one of the components with a component having different characteristics or updated features. Again, both components must be replaced.